With the continuous increase of cross-ocean tunnel engineering, an immersed-tube method for building a subsea tunnel is widely applied. An immersed tunnel is generally formed by transporting a plurality of factory-prefabricated standard tube sections to a sea surface site in a floating manner, jointing the tube sections at the seabed, and immersing them in a dredged foundation ditch. At the present, tube section structures for immersed tunnels which have been built at home and abroad are mainly classified into two types, including a segment type flexible tube section and an integrated type rigid tube section.
The flexible tube section is formed by successively connecting multiple segments in an end-to-end manner, and the segments are connected at segment joint positions through matched tenon structures and gap-crossing buried-in water stop bands. In case of an external load, this structure mainly shows its flexibility characteristic that the segment joints of the tube section are opened and rotate; tube section bending moments are released via deformation; as longitudinal stress on the structure is relatively low, a small number of longitudinal reinforcing bars are provided; however, a portion between tube section segments is low in shear resistance and water resistance to result in a water stop risk between the tube section segments, and a relatively high risk will be caused if the flexible tube section is applied to a high-load or soft-foundation immersed tunnel.
The rigid tube section is an integrated tube section or is formed by connecting multiple tube section segments in an end-to-end manner through bonded prestress. The tube section may resist an external load with its overall rigidity; due to relatively high longitudinal stress on the tube section, it needs to arrange a large number of steel bars or set massive prestress to improve the bearing capacity of the tube section; in addition, the rigid tube section may not redistribute a structural internal force via tube section flexible deformation, so that the stress inside the structure is not uniform, and a region pressed by a relatively high force may have cracking and water leakage risks due to a long-time high stress; and the tube section also may not adapt to a subsea complicated settling environment by itself.